@node unlinkat
@section @code{unlinkat}
@findex unlinkat

POSIX specification:@* @url{https://pubs.opengroup.org/onlinepubs/9699919799/functions/unlinkat.html}

Gnulib module: unlinkat

Portability problems fixed by Gnulib:
@itemize
@item
This function is missing on some platforms:
glibc 2.3.6, Mac OS X 10.5, FreeBSD 6.0, NetBSD 5.0, OpenBSD 3.8, Minix 3.1.8,
AIX 5.1, HP-UX 11, IRIX 6.5, Cygwin 1.5.x, mingw, MSVC 14.
But the replacement function is not safe to be used in libraries and is not multithread-safe.
@item
This function is declared in @code{<fcntl.h>}, not in @code{<unistd.h>},
on some platforms:
Cygwin 1.7.1, Android 4.3.
@item
On Mac OS X 10.10, in a writable HFS mount, @code{unlinkat(fd, "..", 0)} succeeds
without doing anything.
@item
Some systems mistakenly succeed on @code{unlinkat(fd,"file/",flag)}:
GNU/Hurd, Solaris 9.
@end itemize

Portability problems not fixed by Gnulib:
@itemize
@item
When @code{unlinkat(fd,name,AT_REMOVEDIR)} fails because the specified
directory is not empty, the @code{errno} value is system dependent.
@item
POSIX requires that @code{unlinkdir(fd,"link-to-empty/",AT_REMOVEDIR)}
remove @file{empty} and leave @file{link-to-empty} as a dangling
symlink.  This is counter-intuitive, so some systems fail with
@code{ENOTDIR} instead:
glibc
@item
Some systems allow a superuser to unlink directories, even though this
can cause file system corruption.  The error given if a process is not
permitted to unlink directories varies across implementations; it is
not always the POSIX value of @code{EPERM}.  Meanwhile, if a process
has the ability to unlink directories, POSIX requires that
@code{unlinkat(fd,"symlink-to-dir/",0)} remove @file{dir} and leave
@file{symlink-to-dir} dangling; this behavior is counter-intuitive.
The gnulib module @code{unlinkdir} can help determine whether code must be
cautious of unlinking directories.
@item
Removing an open file is non-portable: On Unix this allows the programs that
have the file already open to continue working with it; the file's storage
is only freed when the no process has the file open any more.  On Windows,
the attempt to remove an open file fails.
@end itemize
